The following description is used to describe the background and products, materials and production methods that may comprise specific parts of preferred embodiments in this disclosure.
a) Laminate Floors
The majority of all laminate floors are produced according to a production method generally referred to as Direct Pressed Laminate (DPL). Such laminated floors have a core of 6-12 mm fibreboard, a 0.2 mm thick upper decorative surface layer of laminate and a 0.1-0.2 mm thick lower balancing layer.
The surface layer of a laminate floor is characterized in that the decorative and wear properties are generally obtained with two separate layers of melamine formaldehyde impregnated paper, one above the other. The decorative layer is generally a printed paper that may be digitally printed and the wear layer is a transparent overlay paper, which comprises small aluminium oxide particles. The paper sheets are laminated to a HDF core in large discontinuous or continuous laminate presses where the resin cures under high heat (about 170° C.) and pressure (40-60 bars) and the papers are laminated to the core material. An embossed press plate or steal belt forms the surface structure. Sometimes a structured paper is used as a press matrix. The embossings in high quality floors are made in register with the design.
b) Powder-based Floors.
Recently new “paper free” floor types have been developed with solid surfaces comprising a substantially homogenous powder mix of fibres, binders and wear resistant particles hereafter referred to as WFF (Wood Fibre Floor).
The powder mix may comprise aluminium oxide particles, melamine formaldehyde resins and wood fibres. In most applications, decorative particles such as, for example, colour pigments are included in the mix. In general, all these materials are applied in dry form as a mixed powder on a HDF core and cured under similar heat and pressure as used in laminate floors. Digital powder printing has been developed and it is possible to create very advanced designs of any type by injecting ink into the powder prior to pressing. The surface structure is made in the same way as for laminate flooring by a structured press plate, a steal belt or a paper press matrix that is pressed against the powder.
c) LVT Floors
Luxury Vinyl Tiles, generally referred to as LVT floorings, are constructed as a layered product made of thermoplastic PVC mixed with plasticizers. The name LVT is somewhat misleading since a major part of LVT floors have a plank size with a wood pattern.
Thermal moulding may be based on calendar rolling or extrusion is used to form the PVC layers. During the calendar rolling, the PVC material is heated to its softening temperature and exposed to pressure between cylinders and cooled down. The core is made primarily of several layers that are about 1 mm thick. The layers comprise PVC mixed with chalk and/or limestone fillers. A 0.1 mm high quality printed decorative PVC foil is applied on the upper side of the core. A transparent wear layer of vinyl with a thickness of 0.1-0.6 mm is generally applied on the decorative foil.
When PVC is heated it becomes soft like a paste and bonds under heat and pressure to other PVC materials but also to organic and inorganic fibres or minerals when cooled down to room temperature. The core layer, the decorative foil and the transparent layer are fused or laminated together with heat and pressure in continuous or discontinuous press operations. A transparent UV curing PU (polyurethane) lacquer is generally applied as a protective layer on the transparent PVC foil.
PVC expands under heat and shrinks when cooled down. The dimensional change is considerable within the temperatures that are used during production. Layers that comprise more vinyl expand and shrink more that layers with lower vinyl content. A balancing layer that comprises more vinyl than the middle layers is generally used in the lower part of the core to balance the transparent upper layer comprising primarily only vinyl (such as at least 95% vinyl).
LVT floors and other floor types described above have often an embossed structure and such structure may be a so-called EIR embossing where the décor is made in register with the embossing. The embossing is made with structured rollers or press plates. A high quality EIR embossing requires that a print is adapted to the thermal expansion and shrinkage during production and that the foil is applied with high precision on the core.
The laminated sheets are, after pressing, annealed to remove stress and to achieve increased dimensional stability. Calendar rolling, pressing and annealing general takes place at temperatures between 120° C.-160° C. Annealing may be combined with ageing at temperatures around 25° C.-30° C. during a few days.
PVC in LVT floors may be replaced with other thermoplastic materials. Chalk and or limestone fillers may be partly or completely replaced by other fillers for example wood fibres.
d) WPC Floors
Wood Plastic Composite floors, generally referred to as WPC floors, are similar to LVT floors. The core comprises thermoplastic material mixed with wood fibre fillers and is generally stronger and much more rigid than the mineral-based LVT core. A printed image is protected by a transparent foil or a UV-curable lacquer in the same way as in LVT floors. EIR may also be used.
Thermoplastic material such as PVC, PP or PE may be combined with a mix of wood fibres and mineral particles and this may provide a wide variety of floor panels with different densities and flexibilities.
The decorative effects in LVT and WPC floors may be obtained with a thermoplastic decorative foil that is printed separately and fused on the core layers. The foil comprises a single colour that generally is white and covers the dark colour of the core. The foil provides a base colour for the rotogravure printing process where special solvent-based inks are used to create wood, tile and stone designs. A digital print may also be applied directly on a LVT or WPC core material. Digital printing of LVT and WPC floors is only on an experimental stage since it is difficult to print on the plastic foil and plastic core but would, if introduced, provide major advantages over conventional printing technology.